/*!
 * This code is developed based on an answer from Omnifarious
 * on the stackoverflow.
 * (https://stackoverflow.com/questions/5288076/base64-encoding-and-decoding-with-openssl)
 */
#include "base64.h"

#include <algorithm>
#include <cmath>
#include <iostream>
#include <string>

static const char b64_table[65] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static const char reverse_table[128] = {
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 62, 64, 64, 64, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60,
    61, 64, 64, 64, 64, 64, 64, 64, 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10,
    11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64,
    64, 64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
    43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64};

std::string base64_encode(const ::std::string& bindata) {
  using ::std::numeric_limits;
  using ::std::string;

  if (bindata.size() > (numeric_limits<string::size_type>::max() / 4u) * 3u) {
    throw ::std::length_error("Converting too large a string to base64.");
  }

  const ::std::size_t binlen = bindata.size();
  // Use = signs so the end is properly padded.
  string retval((((binlen + 2) / 3) * 4), '=');
  ::std::size_t outpos = 0;
  int bits_collected = 0;
  unsigned int accumulator = 0;
  const string::const_iterator binend = bindata.end();

  for (string::const_iterator i = bindata.begin(); i != binend; ++i) {
    accumulator = (accumulator << 8) | (*i & 0xffu);
    bits_collected += 8;
    while (bits_collected >= 6) {
      bits_collected -= 6;
      retval[outpos++] = b64_table[(accumulator >> bits_collected) & 0x3fu];
    }
  }
  if (bits_collected > 0) {  // Any trailing bits that are missing.
    // assert(bits_collected < 6);
    accumulator <<= 6 - bits_collected;
    retval[outpos++] = b64_table[accumulator & 0x3fu];
  }
  // assert(outpos >= (retval.size() - 2));
  // assert(outpos <= retval.size());
  return retval;
}

std::string base64_decode(const ::std::string& ascdata) {
  using ::std::string;
  string retval;
  const string::const_iterator last = ascdata.end();
  int bits_collected = 0;
  unsigned int accumulator = 0;

  for (string::const_iterator i = ascdata.begin(); i != last; ++i) {
    const int c = *i;
    if (::std::isspace(c) || c == '=') {
      // Skip whitespace and padding. Be liberal in what you accept.
      continue;
    }
    if ((c > 127) || (c < 0) || (reverse_table[c] > 63)) {
      throw ::std::invalid_argument(
          "This contains characters not legal in a base64 encoded string.");
    }
    accumulator = (accumulator << 6) | reverse_table[c];
    bits_collected += 6;
    if (bits_collected >= 8) {
      bits_collected -= 8;
      retval += static_cast<char>((accumulator >> bits_collected) & 0xffu);
    }
  }
  return retval;
}
